Portgaz d ace is the son of roger and portgaz d rouge roger's lover, monkey d luffy is the son of monkey d dragon, grandson of monkey d garp ace is adopted by garp. The will of d is still mystery in the anime one piece many great men hav the d in their name whitebeard said that that is fate when one of the Ds dies away then another will pick it up and continue the will then one day that person will carry on their back all the weight in the past decades and challenges the world to a fight that day will come when that person finds One piece, just like roger's will ace's will will be carry on by someone in the fulture, sengoku and the government is afraid of the day when one person found one piece, when that day come the world will turn upside down ( marshall d teach aka blackbeard is NOT the one who is carrying the will of D)
(Fact all the people with will of D died or almost died with a smile)